No line number found known for in gdb

I have compiled my own glibc, which produced libc.so. I loaded the libc.so file in gdb by doing gdb -q ./libc.so. However, when I try to find the location of a function by doing list function_name, I get the error message, No line number known for function_name. Note that I use the -g flag for compiling glibc. How can I solve this problem?

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